Polyimide resins are generally superior in heat resistance and electrical insulating properties, and hence they find use as a raw material for printed circuit boards and heat-resistant adhesive tapes. It also finds use as a resin varnish to be formed into surface-protective film and interlayer insulating film for electrical components and semiconductor materials. Unfortunately, polyimide resins are only soluble in limited kinds of solvents, and consequently they are usually used in such a way that polyamic acid, which is a precursor of polyimide and soluble comparatively easily in various organic solvents, is applied to a substrate and this coating step is followed by high temperature treatment (for cyclodehydration) to give a cured product of polyimide resin.
In order to cope with the process just mentioned above, there has increased a demand for adhesives and coating materials formed from polyimide resin capable of hardening with ultraviolet rays, because the hardening of polyimide resin with ultraviolet rays or visible rays proceeds at a low temperature for a short time. (See Patent Document 1: JP-A 2006-104447.) In addition, the polyimide resin to be used as adhesives and coating materials needs thixotropic properties so that it does not suffer from drooling and cobwebbing and also from spreading at the time of application. Also, there is recently an increasing attention to adhesion to polyolefins having a low surface free energy so as to explore adhesion between different materials, such as between metal and plastics.